Add solutions to challenge 4

basics.ts

@@ -90,3 +90,16 @@ export const crackSingleByteKeyMsg: CrackSingleByteKeyMsg = (msg) => {
     candidates.sort((a, b) => b[0] - a[0]);
     return candidates[0][1];
 };
+
+type DetectSingleByteXor = (buffs: Buffer[]) => string;
+export const detectSingleByteXor: DetectSingleByteXor = (buffs) => {
+    const candidates = [] as [number, string][];
+    buffs.slice(0, -1).forEach(buff => {
+        range(0, 255).forEach(i => {
+            const decrypted = decryptSingleByte(buff, i);
+            candidates.push([scoreBuffer(decrypted), decrypted.toString('utf-8').trim()]);
+        });
+    });
+    candidates.sort((a, b) => b[0] - a[0]);
+    return candidates[0][1];
+};